"It's hard for me, you know, not feeling great and throwing up in front of a bunch of people," Bieber said to a screaming crowd upon his return. "Will you love me even though I'm throwing up on stage? OK, I wanted to give you my best show ever, so do you mind if I finish it?"

And that he did, dedicating "One Less Lonely Girl" to his late fan Avalanna Routh, who passed away from cancer Wednesday.

"Great show. Getting better for tomorrow's show!!!! Love u," Bieber tweeted, along with an instagram pic of himself laying in bed. "And .... Milk was a bad choice! Lol. Goodnight Avalanna. Tonight was for u. I love u."

"The star of the show last night was Bieber, the ultimate professional," Chu said. "And he really impressed me with his honesty to his fans, without hesitation. This guy knows his audience more than anyone."

Chu said the night was very emotional, adding, "And when he told the audience he was not choosing a "one less lonely girl" tonight and instead singing it to Avalanna and sang it to an empty chair with a flower crown on it...The whole audience was bawling. Including me. I don't think I've ever felt that emotional at a concert before."